Active vibratory noise control apparatus

ABSTRACT

When the frequency of an engine rotation signal reaches a predetermined frequency, a comparator of a switching unit outputs a switching control signal to selectors and a filter coefficient updater. Based on the switching control signal, the selector switches from a connection between one memory and a corrector to a connection between another memory and the corrector, thereby changing the transfer characteristics C^rr of the corrector from C^11 to C^10. Based on the switching control signal, the selector switches from a connection between one ADC and a filter coefficient updater to the connection between another ADC and the filter coefficient updater, thereby supplying the filter coefficient updater with an error signal, rather than an error signal.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of Japanese Application No.2006-349257, filed Dec. 26, 2003 the entire specification, claims anddrawings of which are incorporated herewith by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an active vibratory noise controlapparatus for canceling vibratory noises produced by a vibratory noisesource by means of vibratory noise canceling sounds that are opposite inphase to the vibratory noise, and more particularly to an activevibratory noise control apparatus for reducing vibratory noises producedwithin a passenger compartment of a vehicle by a vibratory noise sourcesuch as the vehicle engine.

2. Description of the Related Art

Conventional active vibratory noise control apparatus operate bydetecting noise in the passenger compartment of a vehicle by means of amicrophone disposed centrally over the front seats near the position ofan ear of a passenger, then generating a signal that is opposite inphase to an output signal produced by the microphone based on the noise,and outputting canceling sounds based on the generated signal into thepassenger compartment from two speakers that are mounted respectively inthe left and right doors alongside of the front seats, for therebyreducing the noise at the microphone (see Japanese Laid-Open PatentPublication No. 2003-47097).

As shown in FIG. 3 of the accompanying drawings, when the frequency ofthe sound heard by the ear of the passenger in the passenger compartmentincreases nearly to 140 Hz, for example, one-half of the wavelength ofthe canceling sound becomes nearly (L3-L4), representing the differencebetween a distance L3 from a speaker 28 b on the right side (left sidein FIG. 3) of the vehicle 12, as viewed from the passenger to an earposition 80 of the passenger, and a distance L4 from a speaker 28 a onthe left side (right side in FIG. 3) of the vehicle 12 as viewed fromthe passenger to the ear position 80. At the ear position 80, therefore,the canceling sounds from the speakers 28 a and 28 b interfere with eachother.

According to Japanese Laid-Open Patent Publication No. 2003-47097, aphase shifter generates signals by shifting the central frequency of thephase rotation of the signal in an opposite phase, and supplies thegenerated signals to the respective speakers. In this manner, even whenthe frequency of the sound in the passenger compartment becomes higher,the canceling sounds from the left and right speakers are prevented frominterfering with each other.

However, since the phase shifter is added to the apparatus for reducingnoise in the passenger compartment, and the opposite phase signal isrotated in phase by means of the phase shifter, the active vibratorynoise control apparatus has a complex configuration and is high in cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an active vibratorynoise control apparatus, which has a simple arrangement that is capableof reducing vibratory noise, regardless of changes in frequency of thevibratory noise.

Another object of the present invention is to provide an activevibratory noise control apparatus, which is reduced in cost and iscapable of reducing vibratory noise within a wide space.

According to the present invention, an active vibratory noise controlapparatus basically comprises a reference wave signal generator forgenerating a reference wave signal having a frequency based on thefrequency of vibratory noise generated by a vibratory noise source, anadaptive filter for outputting a control signal based on the referencewave signal in order to cancel the vibratory noise, vibratory noisecanceller for outputting vibratory noise canceling sounds based on thecontrol signal, error signal detector for outputting an error signalbased on the difference between the vibratory noise and the vibratorynoise canceling sounds, corrector for correcting the reference wavesignal and outputting a corrected reference wave signal as a referencesignal to the error signal detector, based on a corrective valuecorresponding to signal transfer characteristics from the vibratorynoise canceller, and filter coefficient updater for sequentiallyupdating a filter coefficient of the adaptive filter in order tominimize the error signal based on the error signal and the referencesignal.

The vibratory noise canceller includes at least two first vibratorynoise canceller disposed near a first space, and at least one secondvibratory noise canceller disposed near a second space. The error signaldetector includes either both at least one first error signal detectordisposed near the first space, and at least one second error signaldetector disposed near the second space, or only the first error signaldetector.

The active vibratory noise control apparatus also includes a switcherfor changing the corrective value of the corrector from a firstcorrective value corresponding to signal transfer characteristics fromthe first vibratory noise canceller to the first error signal detector,or from a second corrective value corresponding to signal transfercharacteristics from the second vibratory noise canceller to the seconderror signal detector, to a third corrective value corresponding tosignal transfer characteristics from the second vibratory noisecanceller to the first error signal detector, and changing the vibratorynoise canceller for outputting the vibratory noise canceling sounds intothe first space from the first vibratory noise canceller to the secondvibratory noise canceller, when control characteristics of the vibratorynoise have changed across a preset threshold value.

With the above arrangement, in order to output the vibratory noisecanceling sounds from the vibratory noise canceller, when the controlcharacteristics of the vibratory noise have changed across the presetthreshold value, the switcher changes the corrective value of thecorrector, and also changes combinations of the vibratory noisecanceller for outputting the vibratory noise canceling sounds and theerror signal detector for outputting the error signal.

Therefore, if the vibratory noise canceling sounds output from two ofthe first vibratory noise canceller tend to interfere with each otherwhen the frequency of the vibratory noise is equal to or higher than apredetermined frequency (e.g., 140 Hz), then the threshold value is setto the predetermined frequency. When the control characteristics of thevibratory noise change across the threshold value, the switcher changesthe combinations of the vibratory noise canceller and the error signaldetector so as to avoid interference between the vibratory noisecanceling sounds. The vibratory noise can efficiently be reduced at alocation spaced from the first error signal detector.

Since the vibratory noise canceling sounds output from the vibratorynoise canceller are prevented from interfering with each other, withoutthe need for the phase shifter disclosed in Japanese Laid-Open PatentPublication No. 2004-47097, vibratory noise can be reduced by a simplerarrangement, even when the frequency of the vibratory noise changes.Also, since a phase shifter is not used, the active vibratory noisecontrol apparatus is relatively low in cost. Since canceling sounds areprevented from interfering with each other by changing combinations ofthe vibratory noise canceller and the error signal detector, vibratorynoises can be reduced within a wider space.

Control characteristics of the vibratory noise are defined bycharacteristics relative to the vibratory noise to be reduced by theactive vibratory noise control apparatus, and may be represented by thefrequency of the vibratory noise, for example. The threshold valuerefers to a threshold value corresponding to the frequency of thevibratory noise, at which the vibratory noise canceling sounds interferewith each other when two of the first vibratory noise canceller outputvibratory noise canceling sounds into the first space.

The first space refers to a space in which vibratory noise is reduced bythe first vibratory noise canceller and the first error signal detectordisposed near the first space when the control characteristics are lowerthan the threshold value, and wherein the vibratory noise is reduced bythe second vibratory noise canceller disposed near the second space whenthe control characteristics are higher than the threshold value. Thesecond space refers to a space in which vibratory noise is reduced bythe second vibratory noise canceller disposed near the second space whenthe control characteristics are lower than the threshold value.

The switcher preferably should stop outputting vibratory noise cancelingsounds from the first vibratory noise canceller when the controlcharacteristics of the vibratory noise have changed across the presetthreshold value. Therefore, the vibratory noise within the first spacecan reliably be reduced even if the control characteristics of thevibratory noise change.

Preferably, the switcher changes the corrective value of the correctorfrom the first corrective value to a fourth corrective valuecorresponding to signal transfer characteristics from the firstvibratory noise canceller to the second error signal detector, and fromthe second corrective value to the third corrective value, changes thevibratory noise canceller for outputting the vibratory noise cancelingsounds into the first space from the first vibratory noise canceller tothe second vibratory noise canceller, and changes the vibratory noisecanceller for outputting the vibratory noise canceling sounds into thesecond space from the second vibratory noise canceller to the firstvibratory noise canceller, when the control characteristics of thevibratory noise have changed across the preset threshold value.Vibratory noises within the first and second spaces can thus reliably bereduced even if the control characteristics of the vibratory noisechange.

Preferably, the switcher includes a control signal supply switcher forchanging the vibratory noise canceller to be supplied with the controlsignal output from the adaptive filter, and an error signal switcher forchanging the error signal detector for supplying the error signal to thefilter coefficient updater, when the control characteristics of thevibratory noise have changed across the preset threshold value.Vibratory noise can thus be reduced efficiently.

Preferably, the vibratory noise source comprises an engine of a vehicle,and the control characteristics of the vibratory noise represent thefrequency of the vibratory noise generated by the engine or by therotational speed of an output shaft of the engine. If the first space isdisposed around the front seats or the rear seat of the passengercompartment of the vehicle, then the vibratory noise in the passengercompartment can reliably be reduced.

Preferably, the vibratory noise source comprises a propeller shaft ortire wheels of the vehicle, and the control characteristics of thevibratory noise represent the rotational frequency of the propellershaft or the tire wheels, or the speed of the vehicle. With thisarrangement, vibratory noises within the passenger compartment can alsoreliably be reduced.

The switcher preferably comprises a corrected filter coefficientcalculator for calculating a corrected filter coefficient by multiplyingthe filter coefficient by a predetermined value of less than 1, and afilter coefficient switcher for supplying the corrected filtercoefficient, rather than the filter coefficient, to the adaptive filterwhen the control characteristics are higher than the threshold value. Inorder to change the vibratory noise canceller for outputting thevibratory noise canceling sounds at the time the control characteristicsbecome higher than the threshold value, the vibratory noise cancellermay be operated in a fade-out mode, for gradually reducing the vibratorynoise canceling sounds rather than stopping output of the vibratorynoise canceling sounds upon changing the vibratory noise canceller.Accordingly, an uncomfortable vibratory noise is prevented from beinggenerated when the vibratory noise canceller are switched.

The switcher may impart hysteresis to the threshold value when thecontrol characteristics are higher than the threshold value and lowerthan the threshold value, so that combinations can be changedefficiently even when the frequency of the vibratory noise varies near afrequency corresponding to the threshold value.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an active vibratory noise control apparatusaccording to a first embodiment of the present invention;

FIG. 2 is a plan view of a vehicle incorporating therein the activevibratory noise control apparatus shown in FIG. 1;

FIG. 3 is a front elevational view showing the layout of speakers and amicrophone near front seats in the vehicle shown in FIG. 2;

FIG. 4 is a plan view of a vehicle incorporating therein the activevibratory noise control apparatus, with a single speaker disposed behinda rear seat in the vehicle;

FIG. 5 is a block diagram of an active vibratory noise control apparatusaccording to a second embodiment of the present invention;

FIG. 6 is a block diagram of an active vibratory noise control apparatusaccording to a third embodiment of the present invention;

FIG. 7 is a block diagram of an active vibratory noise control apparatusaccording to a fourth embodiment of the present invention; and

FIG. 8 is a block diagram of an active vibratory noise control apparatusaccording to a fifth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 through 4 show an active vibratory noise control apparatus(hereinafter referred to as “ANC”) 10A according to a first embodimentof the present invention, which is applied to reduce vibratory noisewithin a passenger compartment (space) 14 of a vehicle 12.

As shown in FIGS. 1 through 3, the ANC 10A includes a microphone (firsterror signal detector) 20 disposed on a roof lining near headrests 18 a,18 b, i.e., near to an ear of a passenger (not shown), centrally overthe front seats 16 a, 16 b in the passenger compartment 14, and anothermicrophone (second error signal detecting means, second error signaldetector) 26 disposed on a roof lining near a headrest 24, centrallyover a rear seat 22 inside the passenger compartment 14.

The ANC 10A also includes a speaker 28 a mounted on a left door near tothe front seats 16 a, 16 b, a speaker 28 b mounted on a right door nearto the front seats 16 a, 16 b, and two speakers 30 a, 30 b disposedbehind the rear seat 22. Alternatively, as shown in FIG. 4, the ANC 10Amay have a single speaker 30 disposed behind the rear seat 22, ratherthan the two speakers 30 a and 30 b. The speakers (vibratory noisecanceller) 28 a, 28 b, 30, 30 a, 30 b shown in FIGS. 1 through 4 areprovided as speakers of an audio system that is incorporated as standardequipment in the vehicle 12.

The ANC 10A also has an ANC controller 32 including a microcomputer. TheANC controller 32 basically comprises a frequency detector 44, areference wave signal generating means (a reference wave signalgenerator) 46, a pair of adaptive filters 48, 54, a pair of filtercoefficient updating means (filter coefficient updater) 52, 58, and apair of correcting means (corrector) 90, 92.

The frequency detector 44 comprises a frequency counter for detectingthe frequency fe of an engine rotation signal that is output from a fuelinjection ECU 42 for controlling an engine 40 on the vehicle 12. Theengine rotation signal is output from a Hall device or the like, notshown, per each revolution of the output shaft of the engine 40. Theengine rotation signal is a signal that correlates with noise generatedfrom the engine 40, e.g., engine sounds and periodic noise caused byvibrational forces produced upon rotation of the output shaft of theengine 40, and vibratory noise caused by vibrations of the engine 40.

The reference wave signal generating means 46 generates a reference wavesignal x of predetermined harmonics with respect to a fundamentalfrequency, which is given as a frequency fe from the frequency detector44.

The adaptive filter 48 generates a control signal S0 by multiplying thereference signal x by a filter coefficient Wfr, and the adaptive filter54 generates a control signal S1 by multiplying the reference signal xby a filter coefficient Wrr. The control signals S0, S1 serve to cancelout vibratory noise (hereinafter referred to as “engine noise”) thatoccurs in the passenger compartment 14 as a result of vibratory noiseproduced from the engine 40. The control signals S0, S1 are converted byDA converters (DACs) 60, 62 from digital signals into analog signals,which are output to the speakers 28 a, 28 b, 30, 30 a, 30 b.

The speakers 28 a, 28 b, 30, 30 a, 30 b output canceling sounds(vibratory noise canceling sounds) into the passenger compartment 14 forcanceling engine noise based on the control signals S0, S1. Themicrophone 20 outputs the difference between the canceling sounds fromthe speakers (first vibratory noise canceling means, first vibratorynoise canceller) 28 a, 28 b or the speakers (second vibratory noisecanceling means, second vibratory noise canceller) 30, 30 a, 30 b andthe engine sound as an error signal e0 to the ANC controller 32. Themicrophone 26 also outputs the difference between the canceling soundsfrom the speakers 30, 30 a, 30 b and the engine sound as an error signale1 to the ANC controller 32.

The correcting means 90 generates a reference signal r0 by correctingthe reference wave signal x with a corrective value, representingtransfer characteristics C^00 (first corrective value) that issimulative of transfer characteristics (first transfer characteristics)C00 from the speakers 28 a, 28 b to the microphone 20, and outputs thereference signal r0 to the filter coefficient updating means 52. Thecorrecting means 92 generates a reference signal r1 by correcting thereference wave signal x with a corrective value, representingpredetermined transfer characteristics C^rr, and outputs the referencesignal r1 to the filter coefficient updating means 58. The transfercharacteristics C^00 are transfer characteristics from the input of theDAC 60 to the output of an AD converter (ADC) 64, including transfercharacteristics C00, and the transfer characteristics C^rr are transfercharacteristics C^11 (second corrective value) from the input of the DAC62 to the output of an ADC 66, including transfer characteristics C11from the speakers 30, 30 a, 30 b to the microphone 26, or transfercharacteristics C^10 (third corrective value) from the input of the DAC62 to the output of the ADC 64,including transfer characteristics C10from the speakers 30,30 a, 30 b to the microphone 20.

Each of the filter coefficient updating means 52, 58 comprises aleast-mean-square (LMS) algorithm processor. The filter coefficientupdating means 52 performs an adaptive calculation process for thefilter coefficient Wfr, based on the reference signal r0 and the errorsignal e0 that has been converted from an analog signal into a digitalsignal by the ADC 64, i.e., a calculation process for calculating thefilter coefficient Wfr, so as to minimize the error signal e0 accordingto an LMS method and thereby update the filter coefficient Wfr. Thefilter coefficient updating means 58 performs an adaptive calculationprocess for the filter coefficient Wrr, based on the reference signal r1and the error signal e0 that has been converted from an analog signalinto a digital signal by the ADC 64 or the error signal e1 that has beenconverted from an analog signal into a digital signal by the ADC 66,i.e., a calculation process for calculating the filter coefficient Wrr,so as to minimize the error signal e0 or e1 according to an LMS methodand thereby update the filter coefficient Wrr.

The ANC controller 32 includes a switching means (switcher) 67 forswitching the transfer characteristics C^rr of the correcting means 92to C^11 or C^10 depending on the frequency fe, and also for switchingthe error signal to be input to the filter coefficient updating means 58to e0 or e1. The switching means 67 comprises a comparator 70, a memory84 for storing the transfer characteristics C^11, a memory 86 forstoring the transfer characteristics C^10, and selectors 82, 88.

The comparator 70 outputs a switching control signal Ss to the selectors82, 88 and the filter coefficient updating means 52, when the frequencyf3 reaches a predetermined frequency (threshold value). Based on theswitching control signal Ss, the selector 82 selectively connects thememory 84 or the memory 86 to the correcting means 92 in order to setthe transfer characteristics C^rr to C^11 or C^10. Based on theswitching control signal Ss, the selector (error signal switcher) 88selectively connects the ADC 64 or the ADC 66 to the filter coefficientupdating means 58, so as to supply the error signal e0 or e1 to thefilter coefficient updating means 58. The filter coefficient updatingmeans 52 performs an adaptive calculation process for updating thefilter coefficient to Wfr=0. The predetermined frequency referred toabove is 140 Hz, for example.

The predetermined frequency of 140 Hz is employed for the followingreasons: As shown in FIG. 3, the distance from the speaker 28 b to themicrophone 20 is represented by L1, the distance from the speaker 28 ato the microphone 20 is represented by L2, the distance from the speaker28 b to the ear position 80 of the passenger near the left door (theright door as viewed in FIG. 3) is represented by L3, and the distancefrom the speaker 28 a to the ear position 80 is represented by L4. Whenthe frequency of the canceling sound increases to nearly 140 Hz,one-half of the wavelength of the canceling sound becomes nearly(L3-L4). As a result, the canceling sounds from the speakers 28 a, 28 binterfere with each other at the ear position 80. However, in thevicinity of the microphone 20, even when the frequency of the cancelingsound reaches 140 Hz, the canceling sounds from the speakers 28 a, 28 bdo not interfere with each other because L1=L2.

The ANC 10A according to the first embodiment is constructed asdescribed above. Operations of the ANC 10A, including switchingoperations of the switching means 67, shall be described below withreference to FIGS. 1 through 4.

A mode of operation of the ANC 10A when the frequency fe is smaller than140 Hz (fe<140 Hz) will first be described below.

The fuel injection ECU 42 outputs an engine rotation signal to the ANCcontroller 32, and the microphones 20, 26 output respective errorsignals e0, e1 to the ANC controller 32. The comparator 70 monitorswhether the frequency fe has reached 140 Hz or not. If the comparator 70judges that fe<140 Hz, then the comparator 70 does not output theswitching control signal Ss to the selectors 82, 88 and the filtercoefficient updating means 52. The selector 82 connects the memory 84 tothe correcting means 92, and the selector 88 connects the ADC 66 to thefilter coefficient updating means 58. As a result, the transfercharacteristics C^rr of the correcting means 92 are set to C^11, and theerror signal e1 is supplied to the filter coefficient updating means 58.The filter coefficient updating means 52 performs an adaptivecalculation process for the filter coefficient Wfr based on thereference signal r0 and the error signal e0, thereby updating the filtercoefficient Wfr. The filter coefficient updating means 58 performs anadaptive calculation process for the filter coefficient Wrr based on thereference signal r1 and the error signal e1, thereby updating the filtercoefficient Wrr.

When fe<140 Hz, therefore, the adaptive filters 48, 54 output respectivecontrol signals S0, S1 through the DACs 60, 62 to the speakers 28 a, 28b, 30, 30 a, 30 b. The speakers 28 a, 28 b output canceling sounds,based on the control signal S0, into a first space around the frontseats 16 a, 16 b in the passenger compartment 14. The speakers 30, 30 a,30 b output canceling sounds, based on the control signal S1, into asecond space around the rear seats 22 inside the passenger compartment14.

The microphone 20 generates the error signal e0, representing thedifference between the canceling sounds from the speakers 28 a, 28 b andthe engine noise, and the microphone 26 generates the error signal e1,representing the difference between the canceling sounds from thespeakers 30, 30 a, 30 b and the engine noise.

When fe<140 Hz, the first space refers to a space in which engine noiseis reduced by the speakers, serving as the first vibratory noisecanceling means, and the microphone, serving as the first error signaldetecting means disposed near the first space. When fe≧140 Hz, the firstspace refers to a space in which engine noise is reduced by thespeakers, serving as the second vibratory noise canceling means disposednear the second space. When fe<140 Hz, the second space refers to aspace in which engine noise is reduced by the speakers, serving as thesecond vibratory noise canceling means disposed near the second space.

A mode of operation of the ANC 10A when the frequency fe is equal to orlarger than 140 Hz (fe≧140 Hz) will be described below.

When the frequency fe reaches 140 Hz, the comparator 70 outputs aswitching control signal Ss to the selectors 82, 88 and the filtercoefficient updating means 52. The selector 82 connects the memory 86 tothe correcting means 92, thereby changing the transfer characteristicsC^rr of the correcting means 92 from C^11 to C^10. The selector 88connects the ADC 64 to the filter coefficient updating means 58, whichis supplied with the error signal e0. The filter coefficient updatingmeans 52 performs an adaptive calculation process for updating thefilter coefficient Wfr of the adaptive filter 48 to Wfr=0.

When fe≧140 Hz, therefore, the ANC controller 32 outputs solely thecontrol signal S1, which is generated by the adaptive filter 54. As aresult, the microphone 20 generates an error signal e0 representing thedifference between the canceling sounds from the speakers 30, 30 a, 30 band the engine noise, while outputting an error signal e0 to the ANCcontroller 32.

With the ANC 10A according to the first embodiment, therefore, if thespeakers 28 a, 28 b, 30, 30 a, 30 b output canceling sounds forcanceling engine noise caused in the passenger compartment 14 as aresult of vibratory noise produced by the engine 40, then in theswitching means 67 when the comparator 70 detects that the frequency feof the engine rotation signal representative of control characteristicsof the vibratory noise has reached a predetermined threshold (near to140 Hz), the comparator 70 outputs a switching control signal Ss to theselectors 82, 88 and the filter coefficient updating means 52. Thetransfer characteristics C^rr of the correcting means 92 are thusswitched to C^11 or C^10 by the selector 82, and the combinations of thespeakers 28 a, 28 b, 30, 30 a, 30 b, which output the canceling sounds,and the microphones 20, 26, which output the error signals e0, e1, arechanged by operation of the selector 88 and the filter coefficientupdating means 52.

When the frequency fe reaches 140 Hz, therefore, the combinations of thespeakers 28 a, 28 b, 30, 30 a, 30 b and the microphones 20, 26 arechanged with the switching means 67 in order to avoid interferencebetween the canceling sounds in the passenger compartment 14. Enginenoise can efficiently be reduced at the ear position 80, which is spacedfrom the microphone 20.

Since canceling sounds are prevented from interfering with each other,without the need for the phase shifter disclosed in Japanese Laid-OpenPatent Publication No. 2003-47097, engine noise inside the passengercompartment 14 can be reduced by means of a simpler arrangementaccording to the first embodiment, even when the frequency fe changes.Further, since a phase shifter is not used, the ANC 10A is relativelylow in cost. Since canceling sounds are prevented from interfering witheach other, as a result of changing the combinations of the speakers 28a, 28 b, 30, 30 a, 30 b and the microphones 20, 26, engine noise can bereduced within a wider space.

When the frequency fe reaches 140 Hz, the comparator 70 outputs aswitching control signal Ss to the selectors 82, 88 and the filtercoefficient updating means 52. Consequently, engine noise in thepassenger compartment 14 can reliably be reduced near the front seats 16a, 16 b (within the first space), even when the frequency fe changes.

Furthermore, when the selector 88 is supplied with the switching controlsignal Ss, since the selector 88 of the switching means 67 switches theerror signal that is supplied to the filter coefficient updating means52 to e0 or e1, engine noise inside the passenger compartment 14 can bereduced efficiently.

An ANC 10B according to a second embodiment of the present inventionwill be described below with reference to FIG. 5. Parts of the ANC 10Bthat are identical to those of the ANC 10A according to the firstembodiment (see FIGS. 1 through 4) shall be denoted using identicalreference characters, and will not be described in detail below.

The ANC 10B differs from the ANC 10A according to the first embodiment(see FIG. 1) in that a correcting means 50 has transfer characteristicsC^fr, and a correcting means 56 has transfer characteristics C^11 (firstcorrective value). The comparator 70 can supply the switching controlsignal Ss to selectors 72, 78 and the filter coefficient updating means58. The selector 72 connects a memory 74 or a memory 76 to thecorrecting means 50 in response to the switching control signal Ss, andthe selector 78 connects the ADC 64 or the ADC 66 to the filtercoefficient updating means 52 in response to the switching controlsignal Ss. The ANC 10B also differs from the ANC 10A in that the firstspace is defined as a space near the rear seat 22 within the passengercompartment 14, whereas the second space is defined as a space near thefront seats 16 a, 16 b within the passenger compartment 14.

The ANC 10B operates as follows: When the frequency fe reaches 140 Hz,the comparator 70 outputs a switching control signal Ss to the selectors72, 78 and the filter coefficient updating means 58.

The selector 72 switches from a connection between the memory 74 forstoring the transfer characteristics C^00 (second corrective value) andthe correcting means 50, to a connection between the memory 76 forstoring transfer characteristics C^01 (third corrective value) from theinput of the DAC 60 to the output of the ADC 66, including transfercharacteristics C01 from the speakers 28 a, 28 b to the microphone 26and the correcting means 50. Thus, the selector 72 changes the transfercharacteristics C^fr of the correcting means 50 from C^00 to C^01. Theselector 78 switches from a connection between the ADC 64 and the filtercoefficient updating means 52, to a connection between the ADC 66 andthe filter coefficient updating means 52, so that the error signal e1can be supplied to the filter coefficient updating means 52.

When fe<140 Hz, the microphone 20 generates an error signal e0representing the difference between the canceling sounds from thespeakers 28 a, 28 b and the engine noise, while the microphone 26generates an error signal e1 representing the difference between thecanceling sounds from the speakers 30 a, 30 b and the engine noise. Whenfe≧140 Hz, the ANC controller 32 outputs only the control signal S0generated by the adaptive filter 48. As a result, the microphone 26generates an error signal e1 representing the difference between thecanceling sounds from the speakers 28 a, 28 b and the engine noise, andalso outputs the error signal e1 to the ANC controller 32.

The ANC 10B according to the second embodiment offers the sameadvantages as those of the switching means 67 of the ANC 10A (seeFIG. 1) according to the first embodiment. In addition, when thefrequency fe reaches 140 Hz, since the switching control signal Ss isoutput to the selectors 72, 78 and the filter coefficient updating means58, engine noise within the first space, near the rear seat 22 insidethe passenger compartment 14, can reliably be reduced even when thefrequency fe changes.

An ANC 10C according to a third embodiment of the present invention willbe described below with reference to FIG. 6.

The ANC 10C is different from the ANCs 10A, 10B according to the firstand second embodiments (see FIGS. 1 through 5) in that when thefrequency fe reaches 140 Hz, the comparator 70 outputs a switchingcontrol signal Ss to the selectors 72, 78, 82, 88 and the filtercoefficient updating means 52, 58.

The ANC 10C according to the third embodiment offers the same advantagesas those of the switching means 67 of the ANCs 10A, 10B according to thefirst and second embodiments. In particular, the ANC 10C can reliablyreduce engine noise within both the first and second spaces, near thefront seats 16 a, 16 b and the rear seat 22 inside the passengercompartment 14, even when the frequency fe changes.

An ANC 10D according to a fourth embodiment of the present inventionwill be described below with reference to FIG. 7.

The ANC 10D differs from the ANC 10B according to the second embodiment(see FIG. 5) in that only one microphone, i.e., the microphone 20, isdisposed in the passenger compartment 14. Further, a selector 96connects the memory 74 or the memory 86 to the correcting means 50 inresponse to the switching control signal Ss, and a selector (controlsignal supply switcher) 98 connects the DAC 60 or the DAC 62 to theadaptive filter 48 in response to the switching control signal Ss. TheANC controller 32 is free of the adaptive filter 54, the correctingmeans 56, the filter coefficient updating means 58, the selector 78, andthe ADC 66. The ANC 10D also differs from the ANC 10B in that the firstspace is defined as a space near the front seats 16 a, 16 b within thepassenger compartment 14, whereas the second space is defined as a spacenear the rear seat 22 within the passenger compartment 14.

The ANC 10D operates as follows: When the frequency fe reaches 140 Hz,the comparator 70 outputs a switching control signal Ss to the selectors96, 98. The selector 96 switches from a connection between the memory 74and the correcting means 50, to a connection between the memory 86 andthe correcting means 50, thereby changing the transfer characteristicsC^fr of the correcting means 50 from C^00 (first corrective value) toC^10 (third corrective value). The selector 98 switches from aconnection between the DAC 60 and the adaptive filter 48, to aconnection between the DAC 62 and the adaptive filter 48. As a result,the filter coefficient updating means 52 updates the filter coefficientWfr based on the transfer characteristics C^10, and the adaptive filter48 outputs a generated control signal, as a control signal S1, throughthe selector 98 and the DAC 62 to the speakers 30 a, 30 b.

When fe<140 Hz, the microphone 20 generates an error signal e0,representing the difference between the canceling sounds from thespeakers 28 a, 28 b and the engine noise. When fe≧140 Hz, the microphone20 generates an error signal e0, representing the difference between thecanceling sounds from the speakers 30 a, 30 b and the engine noise.

The ANC 10D according to the fourth embodiment offers the sameadvantages as those of the switching means 67 of the ANC 10B (see FIG.5) according to the second embodiment. In addition, even though only onemicrophone, i.e., the microphone 20, is disposed inside the passengercompartment 14, engine noise near the front seats 16 a, 16 b within thepassenger compartment 14 (first space) can reliably be reduced,regardless of changes in the frequency fe of the engine rotation signal.Engine noise can efficiently be reduced by supplying control signals S0,S1 from the adaptive filter 48 desirably to the speakers 28 a, 28 b, 30a, 30 b, depending on changes in the frequency fe.

An ANC 10E according to a fifth embodiment of the present invention willbe described below with reference to FIG. 8.

The ANC 10E differs from the ANCs 10A through 10D according to the firstthrough fourth embodiments (see FIGS. 1 through 7) in that the switchingmeans 67 includes the comparator 70, a selector (filter coefficientswitcher) 100, and a corrected filter coefficient calculating means(corrected filter coefficient calculator) 102. In addition, correctingmeans 90, 108 include transfer characteristics, which are setrespectively to C^00 (first corrective value) and C^10 (third correctivevalue).

The corrected filter coefficient calculating means 102 comprises acorrected coefficient setting unit 104, in which a predetermined valueof less than 1 is preset, and a multiplier 106 for multiplying thefilter coefficient Wfr adaptively calculated by the filter coefficientupdating means 52 by the predetermined value, so as to sequentiallycalculate a corrected filter coefficient. As with the ANCs 10A, 10D (seeFIGS. 1 through 4, 7), the first space is defined as a space near thefront seats 16 a, 16 b within the passenger compartment 14, whereas thesecond space is defined as a space near the rear seat 22 within thepassenger compartment 14.

When the frequency fe reaches 140 Hz, the comparator 70 outputs theswitching control signal Ss to the selector 100.

The selector 100 then switches from a connection between the filtercoefficient updating means 52 and the adaptive filter 48, to aconnection between the multiplier 106 and the adaptive filter 48. As aresult, the corrected filter coefficient calculated by the multiplier106 is sequentially updated as the filter coefficient Wfr of theadaptive filter 48.

When fe<140 Hz, the microphone 20 generates an error signal e0representing the difference between the canceling sounds from thespeakers 28 a, 28 b, 30 a, 30 b and the engine noise, and then outputsthe error signal e0 to the ANC controller 32. When fe≧140 Hz, theselector 100 and the corrected filter coefficient calculating means 102update the filter coefficient Wfr, such that the value thereof issequentially reduced. Therefore, canceling sounds output from thespeakers 28 a, 28 b are sequentially reduced, until the canceling soundsoutput from the speakers 28 a, 28 b ultimately are eliminated.

The ANC 10E according to the fifth embodiment is thus capable ofoperating in a fade-out mode for gradually reducing the cancelingsounds, rather than stopping output of the canceling sounds from thespeakers 28 a, 28 b, upon switching of the connection when the frequencyfe reaches 140 Hz. Accordingly, an uncomfortable vibratory noise isprevented from occurring when the speakers are switched.

The above fade-out mode of operation may also be applied to the ANCs 10Athrough 10D, according to the first through fourth embodiments (seeFIGS. 1 through 7).

In the first through fifth embodiments, engine noise inside thepassenger compartment 14 is reduced using the frequency fe of the enginerotation signal. However, the transfer characteristics may also beswitched based on the rotational speed of the output shaft of the engine40.

The vibratory noise source may be a propeller shaft or tire wheels ofthe vehicle 12, whereby the transfer characteristics are switched basedon the rotational frequency of the propeller shaft or the tire wheels,or based on the speed of the vehicle 12, in order to reduce noise fromthe propeller shaft or the tire wheels.

The switching means 67 may be arranged to impart hysteresis to thethreshold value of the comparator 70 when the frequency fe is higherthan 140 Hz and lower than 140 Hz, so that the transfer characteristicscan be switched efficiently even when the frequency fe varies near 140Hz.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made to the embodiment withoutdeparting from the scope of the invention as set forth appended claims.

1. An active vibratory noise control apparatus comprising: referencewave signal generator for generating a reference wave signal having afrequency based on the frequency of vibratory noise generated by avibratory noise source; an adaptive filter for outputting a controlsignal based on said reference wave signal in order to cancel saidvibratory noise; vibratory noise canceller for outputting vibratorynoise canceling sounds based on said control signal; error signaldetector for outputting an error signal based on the difference betweensaid vibratory noise and said vibratory noise canceling sounds;corrector for correcting said reference wave signal and outputting acorrected reference wave signal as a reference signal, based on acorrective value corresponding to signal transfer characteristics fromsaid vibratory noise canceller to said error signal detector; and filtercoefficient updater for sequentially updating a filter coefficient ofsaid adaptive filter in order to minimize said error signal based onsaid error signal and said reference signal, wherein said vibratorynoise canceller includes at least two first vibratory noise cancellerdisposed near a first space, and at least one second vibratory noisecanceller disposed near a second space, and wherein said error signaldetector includes either both at least one first error signal detectordisposed near said first space, and at least one second error signaldetector disposed near said second space, or only said first errorsignal detector; and switcher for changing the corrective value of saidcorrector from a first corrective value corresponding to signal transfercharacteristics from said first vibratory noise canceller to said firsterror signal detector, or from a second corrective value correspondingto signal transfer characteristics from said second vibratory noisecanceller to said second error signal detector, to a third correctivevalue corresponding to signal transfer characteristics from said secondvibratory noise canceller to said first error signal detector, andchanging the vibratory noise canceller for outputting said vibratorynoise canceling sounds into said first space from said first vibratorynoise canceller to said second vibratory noise canceller, when controlcharacteristics of said vibratory noise have changed across a presetthreshold value.
 2. An active vibratory noise control apparatusaccording to claim 1, wherein said switcher stops outputting saidvibratory noise canceling sounds from said first vibratory noisecanceller when the control characteristics of said vibratory noise havechanged across said preset threshold value.
 3. An active vibratory noisecontrol apparatus according to claim 1, wherein said switcher changesthe corrective value of said corrector from said first corrective valueto a fourth corrective value corresponding to signal transfercharacteristics from said first vibratory noise canceller to said seconderror signal detector, and from said second corrective value to saidthird corrective value, changes the vibratory noise canceller foroutputting said vibratory noise canceling sounds into said first spacefrom said first vibratory noise canceller to said second vibratory noisecanceller, and changes the vibratory noise canceller for outputting saidvibratory noise canceling sounds into said second space from said secondvibratory noise canceller to said first vibratory noise canceller, whenthe control characteristics of said vibratory noise have changed acrosssaid preset threshold value.
 4. An active vibratory noise controlapparatus according to claim 1, wherein said switcher includes a controlsignal supply switcher for changing said vibratory noise canceller to besupplied with said control signal output from said adaptive filter whenthe control characteristics of said vibratory noise have changed acrosssaid preset threshold value.
 5. An active vibratory noise controlapparatus according to claim 1, wherein said switcher includes an errorsignal switcher for changing said error signal detector for supplyingsaid error signal to said filter coefficient updater, when the controlcharacteristics of said vibratory noise have changed across said presetthreshold value.
 6. An active vibratory noise control apparatusaccording to claim 1, wherein said vibratory noise source comprises anengine of a vehicle, and said control characteristics of said vibratorynoise represent the frequency of the vibratory noise generated by saidengine or the rotational speed of an output shaft of said engine.
 7. Anactive vibratory noise control apparatus according to claim 6, whereinsaid vehicle comprises a passenger compartment including front seats anda rear seat disposed therein, and wherein if said first space isdisposed around said front seats, said second space is disposed aroundsaid rear seat, and if said first space is disposed around said rearseat, said second space is disposed around said front seats.
 8. Anactive vibratory noise control apparatus according to claim 1, whereinsaid switcher comprises a comparator, memories for storing saidcorrective value, and selectors for changing connections between saidmemories and said corrector; said comparator outputs a switching controlsignal to said selectors when the frequency based on the frequency ofvibratory noise generated by said vibratory noise source reaches apredetermined frequency; and said selectors change connections betweensaid memories and said corrector based on said switching signal so as toset said corrective value stored in said memories in said corrector. 9.An active vibratory noise control apparatus according to claim 1,wherein said switcher comprises a comparator, corrected filtercoefficient calculator, and a filter coefficient switcher for changingconnections between said adaptive filter and said filter coefficientupdater, or said adaptive filter and said corrected filter coefficientcalculator; said corrected filter coefficient calculator sequentiallycalculates a corrected filter coefficient by multiplying said filtercoefficient, as sequentially updated by said filter coefficient updater,by a predetermined value of less than 1; said comparator outputs aswitching control signal to said filter coefficient switcher when thefrequency based on the frequency of vibratory noise generated by saidvibratory noise source reaches a predetermined frequency; and based onsaid switching control signal, said filter coefficient switcher switchesfrom a connection between said filter coefficient updater and saidadaptive filter to a connection between said corrected filtercoefficient calculator and said adaptive filter, and supplies saidcorrected filter coefficient to said adaptive filter, rather than saidfilter coefficient from said filter coefficient updater.